Petroleum is the world's main source of hydrocarbons used as fuel and petrochemical feedstock. Because of the presence of impurities, crude oil is seldom used in the form produced at the well, but rather, is typically converted in oil refineries into the wide range of fuels and petrochemical appropriate for their intended end-use applications.
While compositions of natural petroleum or crude oils vary significantly, all crudes contain sulfur compounds. Generally, sulfur concentrations in crude oils range from about 0.5 to about 1.5 percent, but may deviate upwardly to up to about 8 percent. When combusted, sulfur containing compounds are converted to sulfur oxides (SOx), considered to be an environmental pollutant. Catalytic oxidation of sulfur and the subsequent reaction thereof with water can result in the formation of sulfuric acid mist, thereby also contributing to particulate emissions. And so, such crudes typically must be desulfurized to yield products, which meet performance specifications and/or environmental standards.
Vanadium may also typically be present in crude oils, mainly in the form of porphyrinic and asphaltenic complexes. In some crudes, the vanadium content can reach 1200 ppm and the porphyrinic vanadium content can vary from about 20% to about 50% of the total vanadium content, depending on the source of the crude. The vanadium present in crude has a deleterious effect on the refinery operations, typically by detrimentally impacting the effectiveness of catalysts typically used in catalytic cracking, hydrogenation and hydrodesulphurization. Further, vanadium present in fuel oil combustion products catalyzes the oxidation of sulfur dioxide to sulfur trioxide, leading to the formation of acid rain. Combustion products of vanadium, V2O5, can adhere to surfaces, leading to corrosion that can be problematic in some applications.
Since asphaltenes tend to form coke and/or consume large quantities of hydrogen, deasphalted oil is typically used as a feedstock into the catalytic cracking process. Conventional processes include the use of propane to deasphalt the crude distillation residues or a resid oil solvent extraction (ROSE) process which utilizes light hydrocarbons chosen from propane, n-butane, and n-pentane. Both of these may also result in the removal of some of the asphaltenic vanadium, nitrogen, and/or sulfur.
However, these conventional processes of deasphalting and demetallization can be suboptimal. For example, both require very large solvent quantities in relation to the hydrocarbon feedstock to be treated, and produce large asphaltene streams. Additionally, their efficiencies and yields may not be satisfactory for some commercial applications. Finally, these conventional processes are typically unable to separate metals that are not totally eliminated with the asphaltene fraction, e.g., vanadium.
Efficient, and more cost effective methods for the removal of asphaltenes and metals, e.g., sulfur and vanadium, from hydrocarbon oils are thus needed.